HEMOLYTIC SERA AND THEIR ANTITOXINS. 201 



one of the active substances of the hemolytic serum to neutralize 

 in order to protect the corpuscles, namely, the alexin. Before 

 heating it must neutralize completely not only the alexin but also 

 the sensitizing substance. 



It is very probable that the antisensitizing substance and the anti- 

 alexin are two distinct substances. An antitoxin supersaturated with 

 sensitizing substance still retains intact its property of neutralizing 

 normal guinea-pig alexin. 



Antihemolytic and antibactericidal properties of the antitoxin : 

 In bleeding three guinea-pigs, the first normal without any treat- 

 ment, the second treated by injection of rabbit blood, the third 

 immunized against cholera vibrio, we know that we shall obtain 

 three different sera each possessing the same alexin. The identity 

 of the alexin of normal serum with that of immune serum is one of 

 the important points in the theory we offered five years ago to ex- 

 plain the mode of action of preventive sera on vibrios, a theory to 

 which we shall later return. Two of these three sera are immune 

 sera, and, although identical as regards alexin, differ profoundly in 

 their antibodies or sensitizing substances. The identity of the 

 alexin in normal and immune sera explains why normal serum can 

 restore the original destructive properties of various heated im- 

 mune sera deprived of their alexin indifferently. If, therefore, we 

 add to normal guinea-pig serum containing alexin an anti-alexin 

 neutralizing this latter substance, the normal serum should become 

 incapable, not only of dissolving sensitized red blood cells, but also 

 of producing a granular transformation in cholera vibrios treated 

 with cholera-sensitizing substance. As our antitoxin neutralizes 

 guinea-pig alexin we should expect it to protect various sensitized 

 cells against the effect of this alexin. Such an antitoxin, therefore, 

 would be both antihemolytic and antibactericidal. 



Experiment confirms these suppositions. On mixing antitoxin 

 (55 degrees) with a certain amount of fresh normal guinea-pig serum 

 we remove both its property of restoring cellulicidal activity to hemo- 

 lytic serum and also the power of restoring the bactericidal property 

 to anticholera serum (55 degrees). But if we use normal rabbit serum 

 instead of normal guinea-pig serum the antitoxin no longer shows 

 any protective property either for vibrios or corpuscles. Although 



